Internet Usage Policy: Clarity and Enforcement
A 5-line letter is not sufficient to address the problem. Management needs to articulate a clear policy on internet usage, specifying what is and is not allowed. If internet usage is to be strictly for business use only, then state it clearly. However, your policy must explicitly outline what is not allowed, such as checking private email, sending jokes, long-winded PowerPoint presentations of pretty cats, using Facebook, checking job portals, searching for property, internet shopping, etc.
Employees also need clear direction on what they can and cannot do. Only then can you take action when they break the rules. You can also direct the IT department to block access to certain sites like Facebook, Hotmail, Yahoo, Amazon, etc.